Field of the Invention
The present invention relates to cards carrying microelectronic circuits on chips (chip cards) and more particularly to chip cards having non-contact data transmission capability.
Electronically readable plastic cards that are currently employed preferably work according to two methods. Cards having magnetic stripes that contain no microprocessor chip (chip) for storage and processing of information are most widespread. Cards that contain a chip in which information can be reliably stored and electronically modified are being increasingly utilized. These cards are referred to as chip cards or smart cards. Supplying the chips required on the card with current and voltage occurs via contacts or occurs contact-free according to a method such as set forth in U.S. Pat. No. 4,697,183. Upon employment of the teachings of that patent, chip card systems work contact-free in that energy and data transmission ensue inductively.
The commercially available methods employing the teachings of U.S. Pat. No. 4,697,183 require an extremely close spatial coupling of less than 5 mm distance between the coils on the chip card and the coils in the write/read system. This tight coupling is desirable in many instances in order to make it impossible for unauthorized persons to interrogate the data of a card over a distance.
However, applications are also desirable wherein the card is intended to output its information over a greater distance. This is particularly the case given pure identifications when it is only a matter of acquiring a characteristic card number, as required in the case of access controls.